A room-temperature-curable organopolysiloxane composition has been widely used for a condensation-curable silicone-based sealing agent, an adhesive, a composition for an automobile oil seal, and so on, in various fields such as building, electric and electronic field, transport aircraft, electrical component, and household appliance. Generally, the room-temperature-curable organopolysiloxane composition for these uses achieves good curability by adding an organotin compound or an organotitanium compound as a curing catalyst.
Recently, however, a product containing an organotin compound tends to be unfavorably used because of toxicity of this compound, and it has been forbidden in EU countries since 2012 to use the product containing the compound over 0.1% in terms of tin.
Moreover, when the composition contains an organotin compound, a main chain of the organopolysiloxane is cut, which causes problems of cracking and the reduction in hardness over time. When the composition contains an organotitanium compound, there are problems of low curing rate and discoloration that a resulting cured product (rubber) discolors over time.
For these problems, a composition curable without an organotin compound is in urgent need of development in recent years. As alternative compounds, many bismuth compounds have been studied.
Patent Document 1 describes that a divalent bismuth carboxylate is effective as a curing catalyst for a polyoxyalkylene polymer having a hydrolysable silicon group. Patent Document 2 describes that it is effective to use two compounds selected from a divalent organotin compound, a tetravalent organotin compound, and an organobismuth compound in combination. Furthermore, Patent Document 3 describes that it is effective to use both a Lewis acid and a bismuth compound, and Patent Document 4 describes that a carboxylate of a metal other than tin is effective. However, compositions disclosed in these Patent Documents exhibit insufficient curing rate, and there is no description regarding the application to silicone. Moreover, Patent Document 5 describes bismuth compounds as examples of a curing catalyst for a terminal urea-modified polymer, but fails to describe the application to silicone.
Patent Document 6 suggests that an organic polymer having hydrolysable silyl groups at terminal and side chain is cured by a mixed catalyst composed of a bismuth compound and a reaction product of carboxyl group with amino group so that the composition achieves fast curability. In this disclosure, deep-section curability and fast curability are improved by utilizing water which is a by-product of the ketimine formation with the carboxyl group and the amino group. However, although deep-section curability and fast curability are excellent, there are problems of discoloration due to the reaction product of the carboxyl group with the amino group and reduction in curing properties when the adding amount of the carboxyl group and the amino group are changed.
Patent Document 7 describes that it is effective to use both an iron chelate compound and a bismuth compound as curing catalysts, but since the iron chelate compound is a colored material, a problem that a resulting composition is colored occurs. Patent Document 8 suggests a composition in which a bismuth compound is applied to silicone as a catalyst. This composition can give good fast curability indeed, but has a problem that physical properties of a resulting cured product are changed over time.
Patent Document 9 describes that bismuth catalysts of chelate type are effective, but these catalysts have problems of low curing rate and poor availability. As to a two-component or multicomponent composition, Patent Documents 10 and 11 describe that it is effective to use a bismuth compound as a catalyst, but both cannot be applied to one packaging type. Moreover, Patent Document 10 fails to describe applications to silicone, and in Patent Document 11, since an iron compound is essential besides a bismuth compound, following problems occur: two catalysts are required, and thus the formulation is complicated; a resulting composition is colored, like Patent Document 7.